What happens next?

How to care for pet fiddler crabs 
Provide your crabs a good home. 
Fiddler crabs should not be kept with fish. People have kept them underwater successfully, but these crabs don't live in water, they live on beaches, but enter the water as well.

OPT: [-] If you are keeping them outside, keep them in water with sturdy walls. Do not place them on dangerous surfaces. [-] Always give your crabs clean water to drink (tap water, specifically). Make sure your crabs are fed raw meat, and be gentle with them. [-] Be mindful of space at all times. Fiddler crabs must have space to shed their fur, pupate, and sing. [-] Their entire tank should be damp sand, with an area of at least 1-2 " of water for part of the tank. A 10 gallon (37.9 l) tank could contain 1-2 gallons (3.8-7.6 l) of water.
Their entire tank should be damp sand, with an area of at least 1-2 " of water for part of the tank. A 10 gallon (37.9 l) tank could contain 1-2 gallons (3.8-7.6 l) of water.